A 96-well plate has been precoated with Bordetella pertussis antigens to bind cognate antibodies. Controls or test samples are added to the wells and incubated. Following washing, a horseradish peroxidase (HRP) labelled anti-Human IgA conjugate is added to the wells, which binds to the immobilized Bordetella pertussis-specific antibodies. TMB is then catalyzed by the HRP to produce a blue color product that changes to yellow after adding an acidic stop solution. The density of yellow coloration is directly proportional to the amount of Bordetella pertussis IgA sample captured in plate.